You mean, "Why is OSM better in many places than Google Maps?" Because asking why Google Maps might be better, given the hundreds of millions of dollars invested by their data partners over the past, oh, say, 25 years (NAVTEQ at least), compared to a 5 year old volunteer project done with practically no funding, seems a bit disingenuous.
–
Christopher SchmidtFeb 11 '11 at 9:21

7

OpenStreetMap does have better data in places where people have taken the time and care to go out in the real-world and map what they see - London, UK has many mapping parties a month and the detail is over 70% more than Google Maps - openstreetmap.org/… - all depends on the area your looking at.
–
Mapperz♦Feb 11 '11 at 15:26

4

If you want to compare yourself: tools.geofabrik.de/mc (on one side choose Google Maps, on the other side OSM, then zoom).
–
markusNMar 22 '11 at 19:27

1

With respect to the tile of the question: you can't compare generic "free" and "commercial" data and get a meaningful answer. The field is too wide, and the free/commercial distinction is orthagonal in any case. Some commercial data sets are worse than horrible, others are beyond compare. We could get meaningful answers by asking "how does XXX compare with YYY (for the purpose of ZZZ)?".
–
matt wilkieMay 9 '11 at 16:38

+1 although Wikipedia is often regarded now as comparable or better than the same subjects in published encyclopedias, so maybe in time (and with MS funding - and the MS/Nokia partnershop announced today) the same will happen with OSM.
–
geographikaFeb 11 '11 at 13:01

2

Actually, to my knowledge, MapQuest is the company that has actually pledged and paid the most money to support OSM.
–
DavidFFeb 11 '11 at 15:52

Quality as Currency - In many areas OSM is more current than commercial operations. However the level of currency is not necessarily known. Commercial mapping operations will typically publish periodic updates.

Quality as precision - The precision of data depends on what the mapping is intended to be used for. Large scale topographic mapping is likely to be of much higher precision than equivalent OSM data. The precision of OSM data is by its very nature more variable.

Quality as completeness - In some areas such as developing countries OSM is much more complete. Where commercial data is available it will typically be more complete than the equivalent OSM data, but only within the specification defined by the surveyors.

OSM and commercial mapping data can be compared in terms of objective measures. Quality is too broad a term, and always depends on what you want to do with the data.

If you live in the US you will often find that now that Google has switched to using it's own data instead of Navtech's that the quality of Google maps is way behind OSM for the same area. Google's appears to be an import from US Govt sources (TIGER, USGS etc) but with out the volunteer fixes that that OSM has benefited from.

Actually I think in most places in the US Google us using their own data that they collected when making streetview. I've actually found it is the best source in a few places, position and address/routing. It's the only service that gets to my house....

Most street data started from the Census data, ex Navtec. Even OSM imported the census data. Had the census saw (in those days) that their data was to be used as it has been, I wonder if they would have done a better job.